Test table for measuring lateral forces and displacements

ABSTRACT

A test table for measuring lateral forces and displacements while simultaneously applying, if necessary, normal forces, particularly in nanoidenters and in scratch and wear testers. The test table is mounted in a manner that enables it to be laterally displaced, and the lateral force and displacement can be determined by means of a measured-value acquisition. The test table is fixed between at least two vertically upright leaf springs, which can be laterally deflected in the direction of the lateral (horizontal) motion of the test table to be effected.

CROSS REFERENCE TO RELATED APPLICATIONS

Applicants claim priority under 35 U.S.C. §119 of German Application No.102 49 767.2 filed Oct. 24, 2002. Applicants also claim priority under35 U.S.C. §365 of PCT/DE2003/003556 filed Oct. 23, 2003. Theinternational application under PCT article 21(2) was not published inEnglish.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a test table for measuring lateral forces anddisplacements.

Measurement of the lateral forces and displacements takes place with thesimultaneous application of normal forces, and is used, in particular,in nano-indenters as well as in scratch and wear testers.

In the case of these devices, a normal force is usually applied to asample to be tested, by way of a diamond testing body, and thedisplacement caused by the normal force is measured. In addition, thetest table is moved laterally under the test body, to achieve a relativemovement. The force required for this and the size of the lateraldisplacement are measured.

2. Prior Art

WO 02/16907 A1 describes a device for testing scratch resistance(scratch tester). The test table is mounted to be tangentially movable,whereby the mobility is achieved by means of two C-shaped bend partsthat are provided with notches on the inside edges, in each instance.The tangential force exerted on the sample by the scratch tool isdetected on the test table by way of a measured-value transducer. WO99/46576 relates to a device for measuring the scratch resistance ofcoatings (scratch tester), which possesses an indenter part and a testtable. The test table consists of a clamping device for the sample,which is attached to an I-shaped block, which in turn was affixed to aholder device block by way of four horizontally oriented membranesprings, making the sample laterally movable. The tangential forces aredetected by way of a sensor, while the indenter tip is drawn over thesample surface. As this happens, the springs are not subject to tensilebias. Furthermore, the leaf spring longitudinal direction extendshorizontally and not vertically in the direction of the normal force,resulting in a less advantageous system of action.

SUMMARY OF THE INVENTION

It is the task of the invention to conceive a test table with whichnormal force and displacement as well as lateral force and displacementcan be measured with great accuracy, independent of one another, in eachinstance, whereby the test table itself does not cause anydisplacements, even when great normal forces are in effect.

This task is accomplished with the characterizing features of the firstclaim; advantageous further developments are evident from the dependentclaims.

The test table for measuring lateral forces and displacements, with thesimultaneous application of normal forces, if necessary, particularly innano-indenters as well as scratch and wear testers, is mounted to bemovable laterally, whereby the lateral force and displacement can bedetermined by way of a measured-value acquisition. According to theinvention, the test table is attached between at least two leaf springsthat extend perpendicular in the longitudinal direction of the leafspring and can be deflected laterally in the direction of the lateral(horizontal) movement of the test table that is to be produced.

In this connection, the leaf springs are attached to a frame, preferablyunder bias, at their lower end and at their upper end. Between the lowerend and the upper end of the leaf springs, the test table is suspendedon them, e.g. at specific points. In this connection, the arrangement ofthe test table takes place preferably in the center of the leaf springs,whereby two leaf springs stand opposite one another as a pair of leafsprings. In this connection, it is also possible to mount the test tablebetween several pairs of leaf springs.

The thickness of the leaf springs should be greater than/equal to theirlateral deflection, in order to maintain linearity. It is furthermoreadvantageous if the test table is connected with a damping unit. An oilbath preferably disposed below the test table is used for this purpose,and a damping element disposed on the test table dips into this bath.This damping unit is to be sized in such a manner that vibrations thatcome from the surroundings, in particular, are effectively damped,without any noticeable influence on the desired lateral movement of thetable.

The sample holder is designed to be movable laterally, in order to beable to set the sample surface to the same height even when thethickness of the samples varies.

The measured-value acquisition has a shaft that detects a value close tothe sample, to determine the lateral force and displacement. This shaftis attached vertically in the region between the center of the springsand the sample surface, as well as vertically precisely in the center ofthe sample holder, and serves to displace the table in the lateraldirection as well as to measure this displacement. The shaft can also bemounted on spring elements, and the lateral force can be determineddirectly from their deflection. Measurement of the displacement of theshaft takes place using suitable measurement means (e.g. LVDTs).

Dynamic measurements are also possible, by means of a cyclicdisplacement of the table in the lateral direction. Tribologicalcontacts can be simulated in this manner, e.g. of gear wheels duringtheir movement. The vibrations from the surroundings are reduced bymeans of the damping unit disposed below the test table.

The measured-value acquisition to determine the lateral force anddisplacement can also take place optically.

The solution according to the invention preferably provides for fourleaf springs that stand perpendicular opposite one another, which areattached to a frame under tensile stress. The test table is attached inthe center of the leaf springs, at specific points. As a result, a verygreat normal rigidity and torsion rigidity of the frame and the testtable are achieved.

The test table is therefore suspended in the center of the leaf springs,resulting in the creation of a new and improved type of a principle ofeffect, which is characterized by great torsion rigidity and normalrigidity of both the frame and the test table.

The main advantage of the invention consists in the fact that arelatively great normal force can be applied, without causing anydisplacement of the test table in the normal direction and, at the sametime, a slight lateral displacement of the test table is possible. Inthis connection, the amount of the displacement is preciselyproportional to the deflection of the springs. Furthermore, both normalforce and displacement and lateral force and displacement can bemeasured with great accuracy, independent of one another. In thisconnection, the accuracy that can be achieved is dependent on the sizingof the springs and the resolution of the measured-value transducers. Anyslight normal bending of the system that remains can be detected andcorrected by means of software.

Using the solution according to the invention in a nano-indenter makesit possible to precisely detect the start of crack formation or plasticdeformation in the sample, and thereby to achieve quantitative dataabout mechanical characteristic values of the sample material. It ispossible to achieve a resolution of the lateral displacement below 1 nm,and of the lateral force below 1 μm, using the new type of test table.Furthermore, it is possible, for the first time, to measure lateralforces and displacements that are exclusively caused by the normalforce, and not by a lateral displacement of the sample holder or testbody.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be explained in greater detail in the following,using an exemplary embodiment.

The drawing shows:

FIG. 1: fundamental representation in a top view,

FIG. 2: fundamental representation in the front view according to FIG.1,

FIG. 3: three-dimensional fundamental representation of the attachmentof the springs.

DETAILED DESCRIPTION OF THE DRAWINGS

According to FIGS. 1 and 2, the test table 1, with its verticallyadjustable sample holder 1.1 (can be locked in place by means of acounter-nut 1.2), is attached to a total of four leaf springs 3 thatstand perpendicular, by way of attachment elements 2.1 and longitudinalsupports 2 that extend between the attachment elements 2.1. The fourleaf springs 3 are attached between a frame 4 and a base plate S, underthe effect of an axial bias, at their upper and at their lower ends,whereby the frame 4 sits on the base plate 5. There is an oil pan 6 inthe base plate 5, into which a piston 8 attached to a piston rod 7reaches from the underside of the test table 1, making it possible toachieve damping of the ambient vibrations. In the region verticallybetween two leaf springs 3 and the sample surface (not shown), andhorizontally precisely in the center of the sample holder 1.1, ahorizontal shaft 9 having a tip 9.1 is attached, according to FIG. 2, onwhich two LVDTs are provided and which serves to displace the table inthe lateral direction and to measure the displacement with the LVDTs. Inthis connection, the shaft 9 is mounted on two spring elements 9.2, soas to be axially displaceable. The displacement of the table 1 relativeto the leaf springs 3 is triggered using a piezo-element 10, which isconnected with the LVDTs by way of a horizontal bar 11, which issupported on a spring 12, and by way of a perpendicular bar 13. Thenormal force is applied using an indenter I disposed above the testtable 1.1.

A three-dimensional fundamental representation of the attachment of theleaf springs 3 on the frame 4 and on the base plate 5 is shown in FIG.3. The test table 1, with its sample holder 1.1, is merely indicatedwith a dot-dash line. It sits on two longitudinal supports 2, wherebyeach longitudinal support 2 is connected with a leaf spring 3 standingvertically, at its two ends, by way of attachment elements 2.1 that aremerely indicated. The two longitudinal supports can additionally bereinforced with one another by way of a crosswise support 2.2 (or by wayof a plate, not shown), on which the test table sits. The frame 4, whichconsists of two U-shaped supports 4.1, is disposed on the base plate 5.Each support 4.1 sits on the base plate 5 with two vertical shanks 4.2that are parallel to one another; a horizontal shank 4.3 extends betweenthe two vertical shanks 4.2 of a support 4.1. The upper ends of two leafsprings 3 are attached to each horizontal shank 4.3 of a support 4.1, bymeans of upper clamping jaws S_(o).

Two solid body articulations 14 rest on the base plate 5 at their center14.1, and are attached by means of screws 15, for example. The distanceA between the solid body articulations 14 corresponds to the distancebetween two leaf springs 3 attached on a horizontal shank 4.3, thelength L of each solid body articulation 14 corresponds to the distancebetween opposite leaf springs 3. Each leaf spring 3 is clamped in placeat its lower end, at the corresponding end 14.2 of each solid bodyarticulation 14, by way of lower clamping jaws S_(u). The two ends 14.2of each solid body articulation 14 are spaced apart from the base plate5 by a gap S. Each end 14.2 of a solid body articulation 14 can bebraced by way of bracing elements, not shown, which stand in engagementwith the base plate 5 and the end 14.2 of the solid body articulation inthe direction towards the base plate (direction of the arrow), therebyreducing the gap S and axially biasing the leaf springs 3.

The device for producing the lateral force and the normal force, theindenter, as well as the LVDTs and the oil damping, are not shown inFIG. 3.

As an alternative to the variant shown in FIG. 3, it is also possible tosuspend the test table on only two or three leaf springs, or also onthree or more leaf springs.

1. Test table for measuring lateral forces and displacements, ifnecessary with the simultaneous use of normal forces, particularly innano-indenters as well as in scratch and wear testers, whereby the testtable is mounted to be laterally movable and the lateral force anddisplacement can be determined by way of measured-value acquisition,wherein the test table (1) is attached between at least two leaf springs(3) that stand perpendicular and can be deflected laterally in thedirection of the lateral (horizontal) movement of the test table (1)that is to be produced, and the leaf springs (3) have a bias/tensilestress applied to them and are attached to a frame (4) at their lowerend and at their upper end, and the table is essentially attached to acenter of the leaf springs (3) between their lower end and their upperend.
 2. Test table according to claim 1, wherein the test table (1) issuspended on the leaf springs (3) on a small surface as compared withthe length of the leaf springs (3).
 3. Test table according to claim 1,wherein two leaf springs (3), in each instance, stand opposite oneanother as a leaf spring pair.
 4. Test table according to claim 1wherein the test table (1) is disposed between several leaf springpairs, disposed next to one another.
 5. Test table according to claim 1,wherein the thickness of the leaf springs (3) is approximately greaterthan/equal to their lateral deflection.
 6. Test table according to claim1, wherein the test table (1) is connected to a damping unit.
 7. Testtable according to claim 6, wherein the damping unit is an oil bath (6)disposed below the test table (1), into which a damping element disposedon the test table (1) dips.
 8. Test table according to claim 1, whereinthe test table (1) has a sample holder (1.1) that is structured to bemovable vertically.
 9. Test table according to claim 1, wherein themeasured-value acquisition to determine the lateral force anddisplacement comprises a shaft (9) that engages close to the sample. 10.Test table according to claim 1, wherein the measured-value acquisitionto determine the lateral force and displacement takes place optically.